Alternating-current-direct-current motor circuits



Nov. 17, 1942. c. FREDERICK 2,302,609

ALTERNATING-CURRENT DIRECT-CURRENT MOTOR CIRCUITS Filed May 18, 1940 VINVENTOR Carl L Frederic/v require continuous servicing Patented Nov.17, 1942 UNITED STATES PATENT OFFICE ALTERNATING-CURRENT-DIRECT-CUR-RENT MOTOR CIRCUITS Carl L. Frederick,Fairfield, Conn., assignor toDictaphone Corporation, New York, N. Y., a

corporation of New York Application May 18, 1940, Serial No. 335,901-

3 Claims.

- as, for example, an electric motor, difllculty is encountered inuniversal operation. When such apparatus is connected to an A. C. supplythe reactive characteristic of the load elements causes added impedanceto the flow of current therethrough. and thus decreases the current flowas compared to the flow when the apparatus is connected to-a D. C.supply of equal voltage. If, for satisfactory operation of a loadelement such as a constant speed motor, a substantially constant,predetermined value of current is required on both A. C. and D. C., thenit is necessary to make some provision for increasing the current flowwhen the instrument is connected to an A. C. power supply.

In the past numerous arrangements have been suggested for accomplishingthis effect, but all of these arrangements have necessitated the use ofrelays or switches or other moving parts for altering the connections tovarious circuit elements; such, for example, as those arrangements shownin the U. S. Letters Patent 1,244,510 and 1,244,511 to Benjamin G.Lamme. But, as above-mentioned, all of these previous arrangements havehad the disadvantage of using movable parts or make-and-break" contactswhich and are easily damaged or broken.

It is an object of this invention to provide a simple and efficientelectric circuit arrangement in which an electrical load elementrequiring a substantially constant, predetermined value. of current forproper operation may be operated satisfactorily from either an A'. C. or

. commercial dictating machines.

.ing diagram of the preferred embodiment of the invention applied motor.

Referring to the drawing, this invention is illustratedin connectionwith an electric circuit load element 2 which is here shown as auniversal 'A. C.D. C. constant speed motor such as might be used in thewell-known forms of Such a universal motor is usually of the series typehaving a commutated armature 4' and a field winding 6 connected inseries. .In many instruments where such motors are used, as, forexample, in

to the circuit of a universal dictating machines, it is necessary thatthe 'moa D. C. power supply in an automatic and entirely electricalmanner without the need for switches, relays, or other -m ovingelements.

This and other apparent objects and advantages are obtained by the meansdescribed in the following specification, and may be more tor run at aconstant speed, whether it be connected to an A. C. power-supply or to aD. C. power supply of equal voltage. This necessitates a substantiallyconstant magnetic field condition in the motor, which in turn requires aconstant, predetermined value of current to flow through the armaturewinding 4 and the field winding 6. However, both the armature 4 and thefield 6 are iron-cored coils having a certain amount of inductance whichdevelops an inductive 'reactance when the motor is connected to an A. C.supply, thereby producing added impedance to the flow of current'therethrough. Thus, if the terminals 8 of the motor 2 are connecteddirectly to an A. C... power supply, the current flowing througharmature 4 and field 6 will be much less than if the terminals 8 areconnected to a D. C. power supply of equal voltage. In the past, onemethod of overcoming this change in impedance was to connect a variableresistance in series withthe motor 2 and the power supply, and to use aswitching or sliding contact arrangement which permitted removing mostof this resistance frornthe circuit when the motor was connected to anA. C. supply. Thus, the voltage across the terminals 8 of the motor 2was higher under the A. C. condition than under the D. C. condition, sothat the same current flowed through the motor elements under bothsituations, both supply voltages being equal, even though the totalimpedance of the motor was substantially increasedmoving parts withtheir inherent tendency to set out of adjustment.

In accordance with the embodiment of the present invention hereindescribed, a resistor II is connected in series with the motor armature4 and field 6, across a standard type of plug connector I2 to facilitatethe connection of the motor 2 to any available power supply. A condenserI4 is connected across resistor i0.

By such an arrangement, with a proper choice of values for resistance Iand condenser 14, the circuit is automatically conditioned for operationon either an A. C. or D. C. power supply, so that a substantiallyconstant value of current flows through the windings of motor 2 on bothtypes of power supply, whereby it operates at substantially constantspeed at all times, both supply voltages being equal. This eiiectresults because the condenser ll has substantially no effect for D. C.operation so that the resistance l0, in series with motor armature 4 andfield winding 6, is the current controlling element and its value issuch that the current flow therethrough is limited to the desiredamount. However, when plug i2 is inserted in an A. CJpower supplysocket, condenser H acts as a conductor connecting a relatively lowimpedance across resistor l0 and thus effectively decreases the overallimpedance thereacross. This decrease in the efiective impedance inseries with the motor windings increases the voltage available acrossterminals 8 or the motor and thus compensates for the increase inimpedance of the motor windings due to inductive reactance, so thatsubstantlally the same value of current flows through the motor windingsas under D. C. operation. As an example of values which have been foundto give satisfactory operation with a fractional horse power series typuniversal dictating machine motor, accurate operation has resulted whenresistance H) has a value or 400 ohms and condenser H a capacity 01 6.5microiarads.

As many embodiments might be made of the above invention, and as manychanges might be made in the embodiment above described, it is to beunderstood that all structures hereinbefore described and shown in theaccompanying drawing are to be considered as illustrative only and notin a limiting sense.

I claim:

1. In an electric motor drive system adapted to operate from an A. C. orD. C. power supply and in which a load is to be driven at anapproximately constant speed by a universal series-type motor capable ofoperating from an A. C. or D. C. power supply and having a greateroverall impedance when operated on A. C. than when operated on D. C.,the combination with said motor of a compensating assembly adapted to beconnected between said motor and a power supply comprising acurrent-limiting resistor connected in series with said motor and saidpower supply to limit th current to said motor to its proper operatingvalue when said system is connected to a D. C- P w r supp y. and acondenser connected asoaeoe in parallel with said resistor, saidcondenser being eiiective when said system is connected to an A. C.power supply to reduce the impedance across said resistor and thus theimpedance between said motor and said power supply to compensate for theincreased impedance 0! said motor due to the application of A. C.thereto, whereby the proper operating current is supplied to said motorwhether said system is connected to an A. C. or D. C. power supply.

2. In an electric motor drive system adapted to operate from an A. C. orD.'C. power supply and in which a load is to be driven at anapproximately constant speed by a universal motor capable of operatingfrom an A. C. or D. C. power supply and having a greater overallimpedance when operated on A. C. than when operated on D. C., thecombination with said motor of a compensating assembly adapted to beconnected between said motor and a power supply comprisingcurrent-limiting resistance means connected in series with said motorand said power supply to limit the current through said motor to itsproper operating value when said system is connected to a D. C. powersupply, and capacitive impedance means connected in parallel with saidresistance means, said impedance means being effective when said systemis connected to an A. C. power supply to reduce the potential dropacross said resistance means and thus the drop between said motor andsaid power supply to compensate for the increased impedance oi saidmotor due to the application of A. C. thereto, whereby the properoperating current is supplied to said motor whether said system isconnected to an A. C. or D. C. power supply;

3. In an electrically energized system adapted to be operated from an A.C. or D. C. power supply and in which electric apparatus is to besupplied with electric power at an approximately constant current, saidelectric apparatus being capable of operating on A. C. or D. C. buthaving a greater over-all impedance when operated on A. C. than whenoperated on D. C., the combination with said electric apparatus of acompensating assembly adapted to be connected between said apparatus anda power supply comprising a current limiting resistor connected inseries with said electric apparatus and said power supply to limit thecurrent to said appsratus to its proper operating value when said systemis connected to a D. C. power supply, and a condenser connected inparallel with said resistor, said condenser being effective when saidsystem is connected to an A. C. power supp y reduce the impedance acrosssaid resistor and thus the impedance between said electric appsratus andsaid power supply to compensate for the increased impedance of saidelectric apparatus due to the application of A. C. thereto, whereby theproper operating current is supplied to said electric apparatus whethersaid system is connected to an A. C. or D. C. power supply.

CARL L. FREDERICK.

